The effect of different counter-anions on two nonsymmetric salamo-type copper(II) complexes with different structures

Abstract

A nonsymmetric salamo-type ligand H2L with both N2O2 and O3 cavities was designed and constructed, and single crystals of two copper(II) complexes with completely different structures were grown by coordinating H2L with different copper(II) salts, which were determined as [Cu(L)(H2O)] (1) and [{Cu2(L)(NO3)(H2O)3}2(μ2-NO3)]NO3⋅EtOH (2). In complex 1, penta-coordinated copper(II) atom forms a square pyramidal geometry. However, in complex 2, four copper(II) atoms are all six-coordinated, and form distorted octahedral geometrical configurations. Interestingly, the presence of the counter-anion (NO3−) makes a big difference in the configuration of the complexes. Finally, complexes 1 and 2 with a tetragonal cone configuration in mononuclear five-coordinated and an octahedral structure in tetranuclear six-coordinated were formed, respectively. In addition, theoretical calculations were performed, such as IRI valuations, Hirshfeld surfaces analyses, DFT and ESP. Calculations have further demonstrated the existence of different weak interactions and electronic nature between the ligand and its complexes thus indirectly proving the reason why the complexes are more stable than ligand.